Image forming apparatus that stably guides sheet to transfer nip portion

Abstract

An image forming apparatus includes a housing, a registration roller pair, a first guiding portion, a second guiding portion, a resistor, and a grounding conductive mechanism. The housing is made of metal and has a grounded inner wall. The registration roller pair is located between the paper sheet feeder and the transfer member in the sheet conveyance path, includes a metallic registration roller and a facing roller that is constituted of an elastic material, and rotates in abutting contact with the registration roller, so as to convey the sheet toward the transfer nip portion. The first guiding portion is made of metal. The second guiding portion is made of a conductive resin material. The grounding conductive mechanism electrically conducts the registration roller, the first guiding portion, and the second guiding portion to the inner wall via a resistor.

What is claimed is: 
     
       1. An image forming apparatus, comprising:
 a housing made of metal and having a grounded inner wall; 
 a paper sheet feeder that feeds a sheet; 
 a sheet conveyance path that conveys the sheet fed from the paper sheet feeder in a predetermined conveyance direction; 
 an image carrier that carries a developer image on a surface of the image carrier; 
 a transfer member located facing the image carrier, the transfer member forming a transfer nip portion through which the sheet passes between the image carrier and the transfer member, so as to transfer the developer image onto the sheet; 
 a registration roller pair located between the paper sheet feeder and the transfer member in the sheet conveyance path, the registration roller pair including a metallic registration roller and a facing roller, constituted of an elastic material, rotating in abutting contact with the registration roller, the registration roller pair conveying the sheet toward the transfer nip portion; 
 a first guiding portion disposed in the sheet conveyance path at least either upstream or downstream of the registration roller pair in the conveyance direction, the first guiding portion being made of metal and guiding the sheet; 
 a second guiding portion made of a conductive resin material, the second guiding portion guiding the sheet conveyed by the registration roller pair toward the transfer nip portion; 
 a resistor with a predetermined electrical resistance; 
 a grounding conductive mechanism that electrically conducts the registration roller, the first guiding portion, and the second guiding portion to the inner wall via the resistor; 
 a conveyance unit constituting a part of the sheet conveyance path, the conveyance unit supporting the registration roller pair, the first guiding portion, and the second guiding portion, and being secured to the housing; 
 an electric board disposed in the conveyance unit and including a plurality of electric components, for supplying high voltage to a plurality of image-forming-apparatus internal components; wherein 
 the resistor is disposed on the electric board, and 
 the grounding conductive mechanism is distributively arranged from the registration roller pair, the first guiding portion, and the second guiding portion to the inner wall via the electric board. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein:
 the sheet conveyance path runs along an approximately horizontal direction from the upstream side in the conveyance direction up to the downstream side in the conveyance direction of the registration roller pair; 
 the first guiding portion includes an upstream-side guiding member defining a top surface portion of the sheet conveyance path in the upstream side in the conveyance direction with respect to the registration roller pair; and 
 the upstream-side guiding member turns around a fulcrum located coaxially on a rotation shaft of the registration roller to ensure opening a part of the sheet conveyance path. 
 
     
     
       3. The image forming apparatus according to  claim 1 , wherein:
 the first guiding portion includes a downstream-side guiding member defining a top surface portion of the sheet conveyance path in the downstream side in the conveyance direction with respect to the registration roller pair; and 
 the image forming apparatus further comprises an image forming unit having a bottom surface portion located over the downstream-side guiding member at interval, rotatably supporting the image carrier, and being removably attachable to the housing. 
 
     
     
       4. The image forming apparatus according to  claim 3 , wherein the bottom surface portion of the image forming unit defines the top surface portion of the sheet conveyance path in the downstream side in the conveyance direction with respect to the downstream-side guiding member, and guides the sheet toward the transfer nip portion. 
     
     
       5. The image forming apparatus according to  claim 1 ,
 wherein the grounding conductive mechanism includes: 
 a first conduction portion electrically conducts the inner wall to the electric board, 
 a second conduction portion connected to the electric board and electrically conducted with the first conduction portion in the electric board via the resistor, and 
 a third conduction portion electrically conducts the second conduction portion to the registration roller, the first guiding portion, and the second guiding portion.